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ELECTRICITY

SECTION 1 QUESTIONS

1. The current through 60 ohm resistor in A is (Fig)

a) 0.025 b) 1/30 c) 2/30 d) 1

120 60

60 120

6 V

2. The current through 60 ohm resistor in the following network in A is (Fig)

Fig. 3

4060

30

30

70

50

6V

a) 0.08 b) 0.06 c) 0.04 d) 0.02 3. A uniform wire of resistance 4 ohm is bent into a square loop. The resistance between the midpoints

of its opposite sides would be a) 4Ω b) 2Ω c) 1Ω d) 0.5Ω 4. It is required to get largest amount of heat energy from a resistance wire of length 0.5 m connected

with a battery of negligible resistance. This can be done a) by joining the wire directly to battery b) by cutting the wires in two equal parts and then joining all of them in parallel to the battery c) by cutting the wire in two four equal pieces and then connecting all of them in parallel to the

battery d) by joining only half the wire

5. A silver voltameter and a zinc voltameter are connected in series and current i is passed for a time t liberating w kg of zinc. The mass of the silver deposited is nearly

a) W b) 3.5 W c) 2.4 W d) 1.7 W

6. An electric immersion heater of 1.08 kW is immersed in water. After the water has reached a tempera-ture of 1000C, how much time will be required to produce 100 g of steam ?

a) 50 s b) 420 s c) 105 s d) 210 s

7. Two resistors in parallel have their resistances in the ratio 1:3. A source is connected to the combina-tion. The ratio of heats produced in a given time in the two resistors is

a) 3:1 b) 9:1 c) 1:3 d) 1:9

8. The terminals of battery of emf 12 V and internal resistance 1 Ω are connected to a circular coil of re-sistance 16 Ω at two points distant a quarter of the circumference of the coil. The current flowing through the smaller arc of the circle in A is

a) 3.0 b) 2.25 c) 0.75 d) 0.5 9. A uniform wire of length 5 cm is carrying a steady current. The electric field inside it is 0.2 V/m. The

potential difference across the ends of the wire is a) 0.1 V b) 0.5 V c) 5 V d) 10-2 V

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Physics for IIT-JEE Screening Test 210. Two wires A and B are in series. When heated, the combination has same resistance at all tempera-

tures. A is of germanium. Then B should be of a) carbon b) aluminium c) silicon d) alloy of carbon and silicon 11. A cell of emf X is connected across a resistor R. The potential difference across the wire is measured

as Y. The internal resistance of the cell should be a) X-Y/(R-X) b) (X-Y)R c) (X-Y)R/X d) (X-Y)R/Y 12. A battery of 2 volt emf and internal resistance 1 ohm sends a current of 1 A through an external load.

If two such batteries are connected in series, the current through the same load would be a) 1A b) 2 A c) 1.5 A d) 1.33 A 13. A rectangular loop carrying a current i is situated near a long

straight wire such that the wire is parallel to one of the sides of the loop and is in the plane of the loop. If a steady current i is established in the wire as shown in the fig. 1, the loop will

a) rotate about an axis parallel to the wire’ b) move away from the wire c) move towards the wire d) remain stationary 14. A wire of given length is first bent in one loop and the next it is

bent in three loops. If the same current is passed in both the cases, the ratio of magnetic induction at their centres will be

a) 1:4 b) 1:9 c) 9:1 d) 1:3 15. A circular loop of mass m and radius r is in a horizontal (x-y plane) table as shown in fig 2. A uniform

magnetic field B is applied parallel tro x-axis. The current in the loop, so that its one edge just lifts from the table is

a) mg/πr2B b) mg/πrB c) mg/2πrB d) πrB/mg 16. The magnetic field at the centre of the cube of edge of length a

carrying a current i is a) zero b) (8µoi)/(√2 a) c) (8µoi)/2√2 a) d) (2µoi)/2√2 a) 17. An electron enters along east in a region in magnetic equator. It will

be deflected a) vertically up b) horizontally along east c) horizontally along west d) vertically down 18. A current of i ampere is flowing through a loop of a circle of radius

r metre which subtends an angle θ as shown. The magnetic field at the centre of the loop is

a) µoiθ/4πr b) µoi sinθ/πr2 c) µoi sinθ/2r d) µoiθ/4r 19. If a graph is plotted between magnetic field due to a long straight

conductor and distance, the graph will be a) straight line with positive slope b) straight line with negative slope c) parabola d) rectangular hyperbola 20. A conducting circular loop of radius r carries a constant current i. It is placed in a uniform magnetic

field Bo such that Bo is perpendicular to the plane of the loop. The magnetic force acting on the loop is

a) irBo b) 2πriBo c) zero d) π riBo 21. A proton and electron of equal momentum enter into a uniform field at right angles to the velocity.

The radius of their tracks will be in the ratio a) 1:1840 b) 1840:1 c) 1:43 d) 1:1 22. A charged particle is undergoing a circular motion in a uniform magentic field. The time period is in-

dependent of a) speed b) mass c) charge d) intensity of magnetic field

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Electricity 3

23. A one MeV energy alpha particle describes a circle of radius x in a uniform magnetic field. A proton of the same energy will describe in the same field a circle of radius

a) x b) x/2 c) 2x d) 1.4 x 24. A circular coil of wire having 100 turns and radius 1m is arranged in plane perpendicular to the mag-

netic meridian. A current of 1 A is passed through the coil. A hori-zontal magnetic needle at the centre will show a deflection

a) tan-1 (1.57) b) tan-1 (3.14) c) 0 d) tan-1 (0.85) 25. In the Lorentz force equation F = qv x B,. which of the following is

correct ? a) v and B are always perpendicular b) v and F are always perpendicular c) v and B cannot be parallel d) F and B be parallel 26. A long straight conduct or is bent into the shape as shown in Fig.6 It carries a current i A and the ra-

dius of the circular loop is a m, The magnetic field at the centre of the loop is a) 0 b) µo i/2π a c) µo i(π+1)2π a d) µo i(π-1)/2π a 27. A thin wire is bent to the form of a square loop ABCD.(fig.7) A

battery is connected between A and C as shown in fig. the magnetic induction due to the current in the loop at the centre O

a) points into the plane of the paper b) points along OP, the bisector of angle BOC c) zero d) points out of the plane of the paper 28. The magnetic field produced by any side at the centre of the square

loop in the adjacent figure 8 is of magnitude B. The magnetic field at the centre due to the whole loop is

a) 0 b) 4B c) 2B d) B 29. The magnetic induction at a point P distant 4 cm from a long cur-

rent carrying wire is X tesla. The induction at a distance 12 cm from the same wire would be (in tesla)

a) X b) X/3 c) 9X d) X/9 30. A circular loop carrying a current of i A is bent into a circular coil

of 4 turns.The new magnetic moment of the coil will be a) 4 times the original b) 2 times the original c) 1/4 of the original d) half of the original 31. Two particles X and Y having equal charges, after being accelerated through the same potential differ-

ence, enter a region of uniform magnetic field and describe circular paths of radii R1 and R2 respec-tively. The ratio of mass of X that of Y is

a) (R1 /R2)1/2 b) (R2/R1) c) (R1/R2) d) (R1 / R2)2

32. Am2 has the same dimension of a) IT b) NT c) JT-1 d) NT-1 33. The torque acting in a magnetic needle when it make 300 with a uniform field is x. The torque acting

when it is perpendicular to the field is a) x b) 3x c) 2x d) (3/2) x 34. A thin uniform magnetic needle of period T is broken into n parts of equal length. The period of one

part will be a) nT b) T/n c) n2T d) T/n2 35. Magnetic shielding to an instrument can be provided by covering with a) soft iron b) plastic c) copper d) aluminium 36. Isogonic lines are those which join places of a) zero dip b) zero declination c) equal dip d) equal declination

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Physics for IIT-JEE Screening Test 437. If a dip needle stands horizontal at a place, the place is

a) magnetic meridian b) perpendicular to magnetic meridian c) magnetic pole d) magnetic equator 38. Two magnets placed one over the other oscillate with a period of 16 s. When one of them is reversed,

the period is 8 s. The ratio of their magnetic moments is a) 3;1 b) 1:3 c) 5:3 d) 3:5 39. The susceptibility of a substance is negative. This substance could be a) bismuth b) iron c) nickel d) aluminium 40. Two magnets of same pole strength p but of lengths 3L and 4L respectively are arranged to form a

right angle so that the north pole of one touches the south pole of the other. The moment of the com-bination is

a) pL b) 7 pL c) 5 pL d) 6 pL 41. The correct dip at a place is δ. If the dip is measured in a plane making and angle θ with the magnetic

meridian as δ1 , then δ1 will be a) tan-1 (tanδ cosθ) b) tan-1 (tanδ sec θ) c) tan-1 (tanδ sinθ) d) tan-1 (tanδ cosec θ) 42. The total intensity of earth’s magnetic field at the magnetic equator is 0.4 cgs units. At a place where

the dip needle reads 900, the vertical intensity will be (in cgs units) a) 0.1 b) 0.2 c) 0,.4 d) 0 43. Which of the following substance has magnetism independent of temperature? a) copper b) aluminium c) iron d) manganese 44. Which of the following material shows the property of hysterisis ? a) copper b) cobalt c) aluminium d) silver 45. Which of the following is most suitable for making the beam of a chemical balance ? a) brass b) iron c) aluminium d) nickel 46. The field due to a short magnet on the axis at distance x is n times the field due to the magnet at a dis-

tance 2x. Here n is a) 2 b) 4 c) 8 d) 16 47. Soft iron is used for electromagnets because of a) high limit of magnetic saturation b) large area for hysterisis curve c) large coercivity d) large retentivity 48. Which of the following is a paramagnetic substance ? a) bismuth b) antimony c) water d) chromium 49. A steel wire of length L has a magnetic moment M. It is bent into a semi circular arc. The new mag-

netic moment is a) M/ 2π b) ML/2π c) M/L d) 2 M/π 50. A magnet of moment m is kept in stable equilibrium in a uniform magnetic field of intensity B. If it is

rotated through an angle of 1800, the work done is a) mB b) 2mB c) mB/2 d) zero 51. A line joining all places on the earth having zero magnetic dip is a) magnetic line of force b) magnetic equator c) magnetic meridian d) isoclinic line 52. A magnet falls vertically through a horizontal copper ring. Its acceleration will be a) always less than g b) always greater than g c) always equal to g d) less than g when approaches and greater than g when recedes 53. The phase difference between the flux linkage and gthe induced e.m.f in a rotating coil in a uniform

magnetic field is a) π b) π/2 c) π/4 d) zero 54. The induced emf in a coil of wire produced by motion of a magnet will not depend on a) number of turns in the coil b) area of the coil c) resistance of the coil d) speed of the magnet

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Electricity 5

55. The energy stored in an inductor is in the form of a) electric b) mechanical c) thermal d) magnetic 56. An aeroplane with wing span of 50 m flies at 540 km/h horizontally along north south. The vertical

component of earth’s magnetic field is 0.2 gauss. The induced emf across the wing tips is a) 0.15 b) 15 V c) 1500 V d) 150 V 57. A square loop PQRS of resistance 1 Ω and

side 10 cm is moved perpendicular to a uniform magnetic field of 1 T. The ends of the loop are connected to a net work of resistors as shown in fig. The speed of the loop so that a current of 1 mA flows through it is (in m/s)

a) 10-2 b) 2 x 10-2 c) 20 d) 10 58. A circuit has a coil of self inductance 20 mH and a resistance of 3 Ω. The induced emf in the circuit

when current changes at a rate 5 A/s is (in volt) a) 0.1 b) 0.1/3 c) 0.3 d) 0.2 59. Lenz’s law is a consequence of the law of conservation of a) charge b) momentum c) mass d) energy 60. An electron moves along the line AB which lies in the same plane

as the circular loop of conducting wire as a shown in the fig.2 What will be the direction of the current induced if any in the loop?

a) no current will be induced b) the current will be clockwise c) the current will be anti-clockwise d) there will be an emf but no current 61. In what way should be conductor AB be moved in a magnetic

field such that the current flows as shown in fig. 3. a) vertically up ward b) towards left c) towards right d) vertically downward 62. J A-2 is the unit of a) permeability b) permittvity c) self indction d) energy density 63. A fan leaf of length L rotates in a uniform magnetic field of

intensity B, with a constant angular velocity . The induced emf between the centre and end of the leaf will be

ω

a) B12 ω b) 2 B12 ω c) (1/2)B12 ω d) B 1ω 64. A coil has a self inductance L. If the length and breadth of the

coil are doubled keeping number of turns per unit length constant the self inductance will a) remain same b) become 2 times c) become 4 times d) become 8 times 65. The coefficient of mutual induction between the two coils will not depend on a) number of turns of the secondary b) distance between primary and secondary c) cross sectional area of the primary d) the rate of change of current in the primary

66. The equivalent inductance between points P and Q in fig.4 is

a) 2H b) 6H c) 8/3H d) 4/9H

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Physics for IIT-JEE Screening Test 667. Two coils have self inductances L1 = 8 mH and L2 = 2mH. The current in the two coils are increased

at the same constant rate. At a certain instant the power given to the two coils are same. At that in-stant if currents in the coils are I1 and I2 respectively, then I1/I2 =

a) 4/1 b) 1/4 c) 2/1 d) 1 68. A conducting square loop of side L and resistance R moves in its plane with a uniform velocity v per-

pendicular to one of its sides. A magnetic induction B constant in time and space pointing perpen-dicular to and into the plane of the loop exits everywhere. The current induced in the loop is

a) BLv/R clockwise b) BLv/R anti-clockwise c) BLv/R clockwise d) 2BLv/R anti-clockwise 69. Which of the following has the dimension of time ? a) LR b) L/R c) R/L d) 1/CR 70. Which of the following is not correct ? a) ohm = henry per second b) farad x henry = second2

c) farad = joule/volt d) ohm x farad = second 71. The flux through a closed circuit of resistance 10 Ω varies with time according to the equation φ = 12t2

+ 4t + 1. The induce current in the circuit 1/4 second after start will be (in ampere) a) 10 b) 2.75 c) 0.275 d) 1 72. The emf in an AC circuit is represented by the equation e = 5 sin ωt and current by i = 2 cos

ωt. The average power consumed in the circuit is (in W) a) 10 b) 10√2 c) 0 d) 5√2 73. An alternating voltage of rms value V is applied to a circuit containing a resistor, inductor, and a ca-

pacitor. Four voltmeters are connected across resistor, inductor, apacitor and supply. If their readings are V1, V2, V3 and V respectively, then

a) V1 + V2 + V3 = V b) V12 + V2

2 + V32 = V2

c) V12 + (V2 – V3)2 = V2 d) (V1 – V2)2 + V3

2 = V2

74. If V1 , V2, V3 are instantaneous voltage across the components and V = Vo sinωt supply voltage a) V1 + V2 + V3 = V b) V1

2 + V22 + V3

2 = V2

c) V12 + (V2 – V3)2 = V2

d) (V1 – V2)2 + V32 = V2

75. In figure2 a 6 volt battery is connected to a Neon lamp which needs 10 volts to glow. An inductor L is connected in parallel. When the key K is switched on which of the following happens ?

a) bulb glows immediately but dimly b) bulb first does not glow but glows dim later c) bulb never glow d) bulb glows bright 76. When the current is switched off in the above circuit

in previous a) bulb goes off immediately b) bulb goes off slowly c) bulb keeps on glowing d) bulb turns brighter and goes off 77. An A.C voltage of rms value 200 V is applied to a

circuit containing a resistor of 60 Ω, inductor of re-actance 180 Ω and a capacitor of reactance 100 Ω. The rms value of current in the circuit is (in A)

a) 2 b) 2.8 c) 10/7 d) 10/19 78. The phase difference between current and voltage in the above circuit given in previous question is a) tan-1 (3/4) b) tan-1 (4/3) c) tan-1 (5/3) d) tan-1 ((3/5) 79. The power factor of circuit given in previous question is a) 0.44 b) 0.8 c) 0.6 d) 1 80. The average power consumed by the circuit in watt is a) 400 b) 200 c) 282 d) 240 81. An electro magnetic wave can be produced by a) positive and negative charge b) steady current in a wire c) varying electric current

d) a strong magnet

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Electricity 7 82. An alternating voltage 230 V, 50 Hz is applied to a circuit containing an inductance, resis-

tance and a capacitance. At any moment for rms voltages, a) the total voltage across each when added will be equal to 230 V b) the voltage across each will be 230 V c) the voltage when added across the three should be less than 230 V d) the voltage across the inductance can be greater than 230 V 83. We have a source of red light and a blue light of same power. Then the red light gives photons per

second a) same in number, but of less energy b) more in number, but of less energy c) less in number and of less energy d) more in number and of more energy 84. The instantaneous values of current and voltage in an A.C circuit are I = 4 sin ωt and E = 100 cos[ωt +

(π/3)] respectively. The phase difference between voltage and current is a) 7π/6 b) 5π/6 c) 2π/3 d) π/3 85. An A.C given by e(t) = 282 sin (120π t) is applied across a resistance of 20 Ω. An A.C ammeter con-

nected in series records a current of a) 14.1 A b) 7.05 A c) 10 A d) 5 A 86. Two coils of inductance L1, L2 are connected in series. The value of inductance is equal to L1 + L2 if a) distance between them is large b) distance between them is small c) they are would one over the other d) same always 87. Which of the following is least scattered by a medium a) X-rays b) visible light c) infra red d) radiowaves 88. Take wave length of blue light roughly as 440 nm and that of red light as 660 nm. The ratio of inten-

sity of red light scattered to that of blue light by earth’s atmosphere is nearly equal to a) 2/3 b) 3/2 c) 4/9 d) 1/5 89. Assuming the radius of earth to be 6400 km, the maximum distance to which a TV signal can be re-

ceived on earth using an antenna of height 500 m is equal to a) 80 km b) 80 x √2 km c) 40 x √2 km d) 160 km 90. If we plot a graph between the reactance of a capacitor and frequency of A.C passing through it , the

graph will be a) a straight line having a positive slope b) a straight line having a negative slope c) a parabola d) a rectangular hyperbola 91. Two point charges +q and –q are held fixed at (-d,0) and (d,0) respectively, of (X,Y) coordinate sys-

tem. Then a) E at all points on the Y-axis is along i b) the electric field E at all points on the X-axis, has the same direction. c) dipole moment is 2 pd directed along i d) work has to be done in bringing a test charge from infinity to the origin. 92. A battery is connected between two points A and B on the circumference of a uniform conducting ring

of radius r and resistance R. One of the arcs AB of the ring subtends an angle θ at the centre. The value of the magnetic induction at the centre due to the current in the ring is (fig)

a) proportional to 2 (1800-θ) b) inversely proportional to r3 c) zero only if θ = 1800

d) zero for all values of θ 93. The wire loop PQRSP formed by joining two semicircular wire of radii R1 and R2 carries a current i as

shown in the fig. 3. The magnetic field B at the point C is

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Physics for IIT-JEE Screening Test 8

a) ⎥⎦

⎤⎢⎣

⎡−

πµ

21

0

R1

R1

2I

b) ⎥⎦

⎤⎢⎣

⎡−

πµ

21

0

R1

R1

4I

c) ⎥⎦

⎤⎢⎣

⎡−

µ

21

0

R1

R1

4I

d) ⎥⎦

⎤⎢⎣

⎡−

µ

21

0

R1

R1

2I

94. A proton of mass 1.67 x 10-27 kg and charge 1.6 x 10-19 C is projected with a speed of 2x106 m/s at an angle of 600 to the X-axis . If a uniform magnetic field of 0.104 Tesla is ap-plied along the Y-axis, the path of the proton is

a) a circle of time eperiod π x 10-7 s b) a circle of time period 2π x 10-7 s c) a helix of time period 2π x 10-7 s d) a helix of time period 4 π x 10-7 s 95. H+ , He+ and O2+ all having the same kinetic energy

pass through a region in which there is a uniform mag-netic field perpendicular to their velocity. The mass of H+. He+ and O2+ are 1 amu, 4 amu and 16 amu respec-tively. Then

a) H+ will be deflected most b) O2+ will be deflected most c) He+ and O2+ will be deflected equally d) all will be deflected equally 96. A microammeter has a resistance of 100 Ω and a full scale range of 50 µA. It can be used as a voltme-

ter or as a higher range ammeter provided a resistance is added to it. Pick the correct range and resis-tance combination(s)

a) 50 V range with 10 kΩ resistance in series b) 10 V range with 200 kΩ resistance in series c) 5 mA range 1 Ω resistance in parallel d) 10 mA range with 1Ω resistance in parallel 97. A piece of copper and another of germanium are cooled from room temperature to 80 K. The resis-

tance of a) each of them increases b) each of them decreases c) copper increases and germanium decreases d) copper decreases and germanium increases 98. A battery of internal resistance 4 Ω is connected to the network of resistance as shown. In order to

give the maximum power to the network, the value of R in Ω should be a) 4/9 b) 8/9 c) 2 d) 18

99. The current through a wire changes with time as given by the equation i = t . the correct value of the rms current within the time interval t = 2 to t = 4 s will be

a) A23)dA33)cA3)bA3

100. Two heater wires of equal resistance are first connected in series and then in parallel, to the same source. The ratio of heat produced in them are in that order

a) 2:1 b) 1:2 c) 4:1 d) 1:4 101. The electric flux through a hemispherical surface of radius R placed in a uniform electric field of in-

tensity E parallel to the axis of its circular plane is a) 2RE2 b) 2πR2E c) R2E d) 4/3πR3E 102. To get maximum current in a resistance of 3Ω, one uses n rows of m cells each, connected in parallel.

If the total number of cells is 24 and internal resistance of a cell 0.5 Ω, then a) m = 12 n = 2 b) m = 8, n = 3 c) m = 2 n = 12 d) m = 6, n = 4

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Electricity 9 103. A particle of mass m and charge q is placed at rest in a uniform electric field E and re-

leased along the y-axis. The kinetic energy it attains after moving a distance y is a) 1/2 qEy b) qE2y c) qEy d) 1/2 m(qEy) 104. An electric dipole in a uniform field is slightly disturbed from equilibrium position. Its period of oscil-

lation is p/IE2)dIE/p2)cI/pE2)bpE/I2)a ππππ

105. A house is served by a 220 V supply line. In a circuit protected by a fuse marked 9 A, the maximum number of 60 W lamps in parallel which can be turned on at the same time is

a) 44 b) 20 c) 22 d) 33 106. The unit of thermo electric power is a) W b) VK-1 c) V d) Vs-1

107. A uniform wire of resistance 2 Ω and length 4 m is melted and reformed into a uniform wire of length 2m. Its resistance now will be (in Ω)

a) 2 b) 0.5 c) 4 d) 0.25 108. A particle carrying a charge of 1 C enters into a uniform magnetic field 3 j with a velocity 2j+k. The

force on the particle has magnitude in N and direction respectively a) √7, +x axis b) √7, -x axis c) 3, + x axisi d) 3, -x axis 109. ML2T-3 I-2 is the dimension of a) potential difference b) electric field c) permitivity d) resistance 110. Which of the following is correct ? a) Resistivity = electric field/current density b) Resistivity = current density/electric field c) Resistivity = 1/current density d) Resistivity = current density/potential 111. Four bulbs connected in series consume a total power of P watt. One of the bulbs is fused and the

other three are connected in series to the same source. The total power consumed (in W) is a) P b) 3P/4 c) 8P/3 d) 4P/3 112. The best combination of properties of a metal to make a standard resistor are a) high resistivity and low temperature coefficient b) high temperature coefficient and high linear expansivity. c) low linear expansivity and high temperature coefficient d) low temperature coefficient and high melting point . 113. Two wires A and B of same material have same mass but radii in the ratio 1:2. Their resistance ratio

RA/RB will be a) 1:4 b) 1:8 c) 1:16 d) 16:1 114. A primary and a secondary cell have same emf. Then a) both give same current b) primary gives more current c) secondary gives more current d) cannot be said from the data 115. You are supplied with two resistors. Using them it is possible to get resistance value 9,27,6 and 18

ohms. The resistance of resistors are a) 9 and 18 b) 27 and 18 c) 6 and 18 d) 27 and 6 116. Four cells each of same emf and same internal resistance are connected in series. The combination

gives a current i. If one of the cells is reversed the current decreases by

a) 25% b) 50% c) %3133)d%

3266

117. An ammeter of resistance G reads 1 ampere per division. It is to be converted into an ammeter read-ing n amperes per division. The resistance to be connected in parallel is

a) nG b) G/(n-1) c) G/n d) (n-1)G 118. *Two resistors having resistances R1 and R2 at 0oC and temperature coefficient α1 and α2 respec-

tively are joined in series. Check the correct statement(s): a) This combination will have same resistance at all temperatures if R1α2 = R2α1

b) This combination will have same resistance at all temperatures if R1α1 = R2α2 c) Both resistors should be made of metals

d) One resistor should be made of metal and the other of semi conductor.

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Physics for IIT-JEE Screening Test 10Solve the following problems within a maximum time of 2 minutes

119. What is the reading of the ammeter (A) in figure1? 120. What is a current through 2 ohm resistor in the network shown in fig 2

Fig.1 Fig.2 Fig.3 121. W

hat is the reading of the ammeter A in the fig 3?

Fig 4 Fig.5

122. What is the reading of ammeter A in the figure 4? 123. A uniform circular loop has a resistance of 2 ohm. A straight conduc-

tor of resistance 1 ohm is connected diametrically in this conductor across AB, as shown in figure 5. What is the number of electrons flowing through the section AB (straight) per second ?

124. A battery of emf E and internal resistance 1 ohm is connected as driv-ing cell in a potentiometer. The balancing length of a Daniel cell is found to be L m. If another battery of same emf and internal resis-tance 2 ohm is connected as driving cell, the balancing length of the same Daniel cell will be

a) more than L b) less than L c) equal to L d) cannot be said from the data. 125. Four wires of same material, labelled as P, Q, R, S, lengths in the ratio 1: √2 : √3: 2 and radii also in

the same ratio are available. Which of them would be most suitable for making a fuse wire? a) P b) Q c) R d) S 126. *Which of the following statements are correct? a) the terminal voltage of a cell will always be less than its emf b) the terminal voltage of a cell can exceed its emf under certain conditions c) the terminal voltage of a cell can be less than or greater than its emf d) the terminal voltage of a cell will always be greater than its emf 127. In the adjacent figure two cells of emf E1 and E2 are connected as shown with a resistor 9 ohm. The

terminal voltage across E1 is (in volt) a) 7.66 b) 8.33 c) 8 d) 0 128. In the same fig. terminal voltage across E2 is (in V) a) 12 b) 12.66 c) 11.34 d) 8

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Electricity 11 129. In the same figure the potential difference across the points P and Q is ( in volt)

a) 11.33 b) 11 c) 8.33 d) 3 . 130. In the adjacent figure, the heat developed per second across the 3 ohm

resistor is H. The heat developed across 1 ohm resistor per second is a) H/3 b) 2H/11 c) 11H/2 d) 3H 131. In the adjacent figure the lamp of resistance 4 ohm shines with

maximum brightness. The internal resistance of the cell is (in ohm) a) 4 b) 2 c) 8 d )nearly zero 132. The equivalent resistance between the points A and B in the figure below is (in ohm) a) 1 b) 3/4 c) 4/3 d) 10 133. A heater has three coils in parallel having resistances 100, 100 and 200 ohm with the option of using

any one or all of them. When 200 ohm coil alone is used, the heat required to boil certain mass of water is 5 minutes. When all the three coils are used, the heat required to boil the same amount of water will be ( in minutes)

a) 25 b) 1 c) 5/4 d) 10/3 134. Charge flows at a steady rate through a conductor of non-uniform cross sectional area. Which of the

following remains constant? a) drift speed of electrons b) current density c) current d) all the three 135. *The resistivity of a wire depends on a) its length b) its cross sectional area c) its material d) temperature 136. An electric bulb rated as 500 W at 100 V is to be used in a circuit of supply voltage 150 V. Then for

the bulb to deliver 500 W, a resistance R a) equal to 20 ohm is to be connected in series b) equal to 20 ohm is to be connected in parallel c) equal to 20/3 ohm is to be connected in series d) equal to 10 ohm is to be connected in series 137. A wire is uniformly stretched to two times its length. The conduc-

tance of the wire a) remains the same b) becomes 1/2 c) becomes 1/4 d) becomes 4 times 138. Three cells each of emf E are connected in series to an external re-

sistor of value 10 ohm. The current through the external resistor is i. When the same cells are connected in parallel to the same resis-tor, the current is still i. The internal resistance of each cell (in ohm) is

a) 30 b) 10/3 c) 10 d) 3 139. A conductor has n electrons per unit volume. It has current density j. If specific charge of electron is

K, then the total momentum of n electrons is equal to a) jK b) K/j c) j/K d) j2K 140. Two electrons of speeds v and 2v enter into a uniform transverse magnetic field. The ratio of their

frequencies of circular motion will be a) 1:1 b) 1:2 c) 2:1 d) 1:4 141. A charged particle of mass m moving with a velocity is subjected to a magnetic field of

If this particle continues with the same velocity in the same direction, its momentum is ( all units in SI)

.j1000fieldelectricanandi20

a) 100m b) 50m c) 200m d) (1/50)m

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Physics for IIT-JEE Screening Test 12

142. A cyclotron cannot be used to accelerate a) α particles b) protons c) electrons d) deuterons 143. A circular loop is placed so that its plane is parallel to a uniform magnetic field. In this magnetic

field, it experiences a) a torque b) a force c) both a torque and a force d) neither a torque nor a force 144. A circular loop carrying current is placed perpendicular to a uniform magnetic field. It experiences a) a torque b) a force c) both a torque and a force d) neither a torque or a force 145. Two circular loops are made from wires of lengths in the ratio 1:2 . If they carry same currents, the

ratio of their magnetic moments is a) 1:2 b) 2:1 c) 1:4 d) 4:1 146. In a uniform transverse magnetic field, a charged particle in motion has a) constant momentum and kinetic energy b) varying momentum but constant kinetic energy c) constant momentum but varying kinetic energy d) varying momentum and varying kinetic energy 147. The ratio of magnetic field at the centre of a current carrying circular coil of radius R to the field at a

distance R from the centre along its axis is a) 1:8 b) 1:4 c) 1:2√2 d) √8:1 148. An electron describes a circular orbit of radius r, with a speed v. The magnetic field produced at the

site of nucleus is

0)er2ev

)dr2ve

)cr2

ev)b

r4ev

)a2

o2

oo2

o

π

µπ

µπ

µ

π

µ

149. The final energy of a charged particle coming out of a cyclotron is independent of a) mass of the particle b) charge of the particle c) the magnetic field d) speed of the particle 150. A proton and a deuteron of same kinetic energy enter into a uniform magnetic field. The ratio of radius

of the track of deuteron to that of proton will be a) 1:1 b) √2:1 c) 1:√2 d) 2:1 151. An electron enters into a uniform magnetic field with equal components of velocity parallel and per-

pendicular to the field . The path of electron will be a) a circle b) an ellipse c) a helix d) a straight line making an angle 45o with field 152. In a hollow copper pipe carrying DC, the magnetic field produced will be a) only outside b) only inside c) both inside and outside d) neither inside nor outside 153. A charged particle accelerated by a potential V enters into a uniform magnetic field. The radius of its

path will be proportional to a) V b) 1/V c) V2 d) √V 154. Two long parallel straight conductors at a distance ‘a’ carry equal currents i. If the force between them

is F, which of the following graphs will be a parabola? a) between F and i b) between F and i2

c) between F and a d) between F and 1/a 155. A beam of electrons move from north to south. A straight conductor is held horizontally with current

flowing from north to south below the electron beam. The electron beam will a) be pulled down b) remain unaffected c) be pulled up d) be pulled horizontally 156. Three identical conductors AB, BC, CA are joined to form the

sides of an equilateral triangle and carry same current as shown in the adjacent figure. The magnetic field due to each conductor at the centroid of the triangle of side ‘a’is X. The total magnetic field at the centroid due to all the conductors will be

a) 3X towards the reader b) 3X into the paper c) be zero

d) 3X cos 60o towards the reader e)

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Electricity 13

157. A helium nucleus makes a full rotation in a circle of radius 0.8 m in 2 s. The value of magnetic induc-tion at the centre of the circle (in T) is

a) 10-19/µo b) 10-19µo c) 2 x 10-19/µo d) 2 x 10-10 µo 158. A steel needle of length L has a magnetic moment M. The needle is bent at the mid point so that two

parts are at right angles. The magnetic moment now will be a) M b) M/2 c) 2M d) M/√2 159. A uniform circular loop has a resistance of 4 ohm. It is connected to a battery as shown in fig. The

ratio of resistance of smaller and larger arc is 1:3. When current is passed as shown, the magnetic field at the centre due to the longer arc ABC to the smaller arc AC

a) will be in the ratio 1:3 in the same direction b) will be in the ratio 3:1 in the same direction c) will be in the ratio 1:3 in the opposite direction d) will be zero 160. A tangent galvanometer has a deflection of 45o, for a given cur-

rent i when the coil is in magnetic meridian. If the coil is inclined at an angle 10o with the meridian, the deflection for the same current will be

a) more than 45o b) less than 45o c) 45o d) cannot be said from the data 161. The period of oscillation of a magnet in a uniform field is T. If two such identical magnets are placed

one over the other so that the like poles point in the same direction, the period in the same field will be

a) T/2 b) T c) √2T d) T/√2 162. The magnetic field at a point (P) distant r from one end of a long

straight conductor carrying a current is

ri

)dr4i

)c

r8

i)b

r2i

)a

oo

oo

πµ

πµ

π

µπµ

163. *Check which of the following statements are correct regarding diamagnetism:

a) Diamagnetism is present in all the substances b) Diamagnetism can be explained from Lenz’s law. c) Diamagnetic effect increases with temperature d) Diamagnetic effect of an atom depends on the radius of electron orbits 164. Two long straight conductors P and Q carry currents i and 2i respectively in the same direction. A

third conductor carrying a current i is kept midway between P and Q. Then R a) will remain in equilibrium b) will move towards P c) will move towards Q d) will oscillate between P and Q 165. Which of the following is out of place here with respect to conserva-

tion of energy principle ? a) Lenz’s law b) Kirchoff’s loop theorem c) Recoil of a gun d) Bernoulli’s theorem 166. A war plane is flying in the region of magnetic equator. In which of

the following cases will there be no induced emf on the wings of the plane?

a) when flying vertically b) when flying horizontally c) when climbing up at an angle d) when coming down at an angle 167. A constant current is flowing through a straight conductor from left to right due to a source of emf.

When the source is switched off a) an induced current will flow from left to right b) an induced current will flow from right to left c) no induced current will flow d) cannot be said from the data 168. .The flux linking with a circuit is given by φ= t3+3t-7. The graph between induced emf and time will

be

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Physics for IIT-JEE Screening Test 14 a) a straight line through origin b) a straight line but not through origin

c) a parabola through origin d) a parabola but not through origin 169. A straight wire is held by an insulating handle and moved across a uniform magnetic field . Then a) an emf is induced in the wire b) a current is induced in the wire c) a charge is induced in the wire d) all the three are induced in the wire 170. If the induced emf and the inducing emf are in the same direction, it will violate a) the law of conservation of momentum b) the law of conservation of charge c) the law of conservation of current d) the law of conservation of energy 171. In order to move a conductor in a non-uniform magnetic field with a velocity 2 m/s, energy is spent at

a rate 20 W. The force acting on the conductor is a) 10 N b) 5 N c) 20 N d) 40 N 172. An A.C of frequency 50 Hz and rms value √2 A flows through the primary of a transformer. If mu-

tual inductance between primary and the secondary is 1 H, the maximum induced emf in the secondary is (in volt)

a) 280 b) 400 c) 560 d) 140 173. Two similar circular coaxial loops carrying equal currents in the same direction approach each other

along their common axis. Then a) the current in each loop will increase b) the current in each loop will decrease c) the current in both the loops will remain the same d) current in one loop will increase and that in the other loop will decrease 174. A current is sent through a vertical spring carrying a weight, from top to bottom. The spring a) will stretch more b) will remain as such c) will contract d) will break 175. The self inductance of a coil depends on a) change of flux through the coil b) rate of change of flux through a coil c) cross sectional area of the coil d) number of turns in the coil 176. When a DC is passed through an inductor of self inductance L, the energy stored in it is a) 1/2 Li2 b) Li2 c) 2Li2 d) 0 177. A circuit has a self inductance of 1 H and carries a current of 2A. To prevent sparking when the cir-

cuit is broken, a capacitor which can withstand 400 volts is used. The least capacitance of the capaci-tor is

a) 12.5 µF b) 50 µF c) 25 µF d) 100 µF 178. The maximum mutual inductance between two coils is 6 H and the difference in their self inductance

is 5 H. Then, the sum of their self inductance is (in H) a) 11 b) 13 c) 20 d) 22 179. *If L,Q,R represent inductance, charge and resistance respectively then the units of a) QR/L will be that of current b) Q2R3/L2 will be that of power c) QL/R will be that of current d) Q3R2/L will be that of power 180. A coil of metal wire is stationary in a strong non-uniform magnetic field . Then a) no e.m.f. is induced in the coil b) a varying e.m.f. is induced in the coil but no current c) a constant e.m.f. and a current are induced in the coil d) a constant e.m.f is induced in the coil, but no current. 181. The e.m.f. across the secondary of a transformer will not depend on a) voltage across the primary b) spacing of the primary turns c) core of the primary d) resistance of the secondary 182. Ohm per henry has the dimensions of a) time b) current c) angular velocity d) magnetic flux 183. An AC voltage E = 200√2 sin (100t) is applied to a 1µF capacitor through an AC ammeter. The read-

ing of the ammeter will be (in mA) a) 10 b) 20

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Electricity 15 c) 40 d) 80 184. The phase angle between current and voltage in an AC circuit is

tan-1 (4/3). The power factor of the circuit is a) 3/4 b) 3/5 c) 4/5 d) 0 185. A coil and a magnet move along a common axis as shown in the adjacent figure. In which of the fol-

lowing cases will there be no induced emf in the coil? a) When both move with same velocity in same direction as shown in figure b) When both move with the same velocity in the opposite direction c) When the coil moves with a velocity v while the magnet is at rest d) When the magnet moves with a velocity v while coil is at rest. 186. An AC represented by the equation e = 282 sin (100πt) is applied to the primary of a step up trans-

former whose turns are in the ratio 1:2. If an AC voltmeter is connected across the secondary, the reading of the voltmeter will be

a) 350 V b) 282 V c) 564 V d) 400 V 187. An AC voltage represented by the equation e = 200 sin(100πt) is applied to a circuit which contains a

pure inductor. The time lag between voltage and current in the inductor will be ( in s) a) 1/200 b) 1/100 c) 1/50 d) 1/25 188. The equation for energy density of magnetic field is a) (1/2) µoB2 b) B2/2µo c) B2/µo d) µoB2

189. A conductor of length L and resistance R kept in a uniform magnetic field B is removed from the field with a velocity v. The power spent in this process is

a) B2L2v2/R b) BL2v2/R c)B2L2v2/2R d) BLv/R 190. Three identical coils A,B,C are placed with their planes parallel as shown in the adjacent figure. The

coils A and C carry currents as shown in figure. The coils B and C are fixed while the coil A moves with uniform velocity towards B. Then

a) no current is induced in B by the two coils. b) a clockwise current is induced in B. c) equal currents are induced in B by the two coils which cancels d) an anti-clockwise current is induced in B 191. *An AC voltage of angular frequency ω is applied to a circuit which consists of an inductor of induc-

tance L and a capacitor of capacitance C in parallel. Then across the inductance a) current is maximum when ω2 = 1/LC b) voltage is maximum when ω2 = 1/LC c) current is minimum when ω2 = 1/LC d) voltage is minimum when ω2 = 1/LC 192. In an LCR circuit given below an AC voltage 200V, 50 Hz is

applied. V1, V2, V3 are three volt- meters connected across the resistor, the inductor and the capacitor. A is an ammeter. At resonance the reading of V2 is 300 V. Then the reading of V1 and V3 are respectively

a) 200 V, 100 V b) 300 V, 100 V c) 200 V, 0 V d) 200 V, 300 V 193. If the resistance R = 200 ohm in the above circuit, the

reading of the ammeter A at resonance will be equal to (in ampere)

a) 1 b) 1/4 c) 1.4 d) 2.8 194. If in the above circuit when not in resonance, the volt meter V1 reads 40 V, V2 reads 50 V and V3

reads 20 V. The source voltage is a) 110 V b) 10 V c) 50 V d) 70 V

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Physics for IIT-JEE Screening Test 16195. An AC circuit has voltage and current represented respectively by E = 100 sin(100t) V and I = 100

sin (100t+π/3) mA . The average power dissipated in the circuit is a) 0 W b) 5000 W c) 5 W d) 2.5 W 196. A 1.0 µF condenser is charged to 50 volts. The charging battery is then disconnected and a 10 mH

coil is connected across the capacitor so that it oscillates . What is the maximum current in the coil ? (Assume that the circuit contains no resistance) :

a) 0.25 A b) 0.50 A c) 0.75 A d) 1.00 A 197. When an AC voltage of rms value 240 V is applied to a circuit having a pure inductor, the current

through the circuit is 3 A. When the same voltage is applied to a circuit having a pure resistor, the cur-rent is 4 A. If the same voltage is applied to a circuit having this resistor and inductor in series, the current through the circuit will be ( in A)

a) 3.5 b) 7 c) 1 d) 2.4 198. A capacitor, an inductor are connected to an electric bulb with a source of AC. If the frequency of AC

supplied is increased from a small value, then the brightness of the bulb a) increases b) decreases c) remains the same d) first increases and then decreases 199. If x is the relative permeability and y is the relative permitivity of a medium, the refractive index of

the medium is equal to

a) yx b)

xy1 c) xy d)

xy

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Electricity 17 SECTION 2: ANSWERS

1 b 2 c 3 c 4 c 5 b

6 d 7 a 8 b 9 d 10 b

11 d 12 d 13 c 14 b 15 b

16 a 17 d 18 a 19 d 20 c

21 d 22 a 23 a 24 c 25 b

26 d 27 c 28 b 29 b 30 c

31 d 32 c 33 c 34 b 35 a

36 d 37 d 38 c 39 a 40 c

41 b 42 c 43 a 44 b 45 a

46 c 47 d 48 d 49 d 50 b

51 b 52 a 53 b 54 c 55 d

56 a 57 b 58 a 59 d 60 a

61 d 62 c 63 c 64 d 65 d

66 a 67 b 68 b 69 b 70 c

71 d 72 c 73 c 74 a 75 b

76 d 77 a 78 b 79 c 80 d

81 c 82 d 83 b 84 b 85 c

86 a 87 d 88 d 89 d 90 d

91 a 92 d 93 c 94 c 95 a,c

96 b,c 97 d 98 c 99 a 100 d

101 b 102 a 103 c 104 a 105 d

106 b 107 b 108 d 109 d 110 a

111 d 112 d 113 d 114 c 115 a

116 b 117 b 118 b&d 119 1A 120 0.3A

121 6/11A 122 0 123 1.25x1019 124 a 125 a

126 b,c,e 127 b 128 c 129 d 130 d

131 a 132 a 133 b 134 c 135 c,d

136 d 137 c 138 c 139 c 140 a

141 b 142 c 143 a 144 d 145 c

146 b 147 d 148 a 149 d 150 b

151 c 152 a 153 d 154 a 155 c

156 b 157 b 158 d 159 d 160 a

161 b 162 c 163 a,b,d 164 c 165 c

166 b 167 a 168 d 169 a 170 d

171 a 172 b 173 b 174 c 175 c,d

176 d 177 c 178 b 179 a,b 180 a

181 d 182 c 183 b 184 b 185 a

186 d 187 a 188 a 189 a 190 d

191 b,c 192 d 193 a 194 c 195 d

196 b 197 d 198 d 199 c